Catalyst-filled tubes are widely used in heat exchange reactors where the reaction mixture is heated or cooled by a heat exchange medium passing around the exterior of the tubes. In particular, such reactors are well known and widely used for the catalytic steam reforming of hydrocarbons wherein a mixture of hydrocarbon, typically methane, and steam are passed at elevated pressure over a particulate reforming catalyst disposed within tubes that are externally heated to high temperatures by a hot gas mixture.
In a heat exchange reactor there can be many hundreds of such tubes, which can be up to 15 meters in length, and effective process control is required to maximise the productivity while at the same time ensuring the apparatus is not over-heated. For example, in heat exchange reformers, control of tube-wall temperatures is vitally important to maximise tube lifetimes. Furthermore catalyst overheating can be undesirable. Process control & monitoring by means of installing temperature measuring devices (e.g. thermocouples) within the catalyst tubes has proven difficult because it has not been possible to ensure that the monitoring device has been placed centrally along the entire length of the tubes.